Roadways per Capita in US |The End of Traffic and the Future of Transport
Unpaved roads per capita (and all roads) had been steadily falling, and now appear to be flattening out, as depaving roads becomes more common.
From Levinson and Krizek (2015) The End of Traffic and the Future of Transport.
Figure 1.2 Source: Based on Bureau of Transportation Statistics (2015) National Transportation Statistics Table 1-4: Public Road and Street Mileage in the United States by Type of Surface(a) (Thousands of miles).